Discrimination of shades of gray for different intervals of time. 11 
A glance at the columns giving the averages of correct judg¬ 
ments for differences of norm and comparison amounting to 10° or 
20° of white as well as the general average of these two 
show that so far as discriminations of differences are concerned, the 
correctness of judgment is practically independent of the time inter¬ 
vals. The figures for the D’n experiments indicate neither influence 
of D’n nor of flight of time for objective differences of the stimuli. 
On the other hand, the number of correct judgments for N=V falls 
off irregularly with the time, the drop from 5 sec. being very marked. 
In all these respects the experiments agree more or less closely with 
similar experiments on clangs. (Angell and Harwood, Discrimina¬ 
tion of clangs etc., Amer. Joum. of Psych. XI, 67.) 
Examining the protocol books to see in how far their records 
agree or disagree with those of Ke and Kl, we find the same ten¬ 
dency towards the formation of a scale of brightness as a basis for 
comparison. Bt indeed notes a great deal of visual imagery, usually 
of the disc or details immediately connected with it. Sometimes this 
is a simple image of the norm, called up when the signal for the 
comparison is given, sometimes it is a persistent image of the disc 
waxing and waning in brightness, and sometimes it is a photism, as 
when he had a bright image of »pale freckled face formed out of 
the image of the norm«, lasting the entire time interval (60 sec.). In 
this connection it may he said that during the first half of the work, 
Bt complained of a play of after-images. Sensations of tension also 
enter largely into Bt’s consciousness during the time interval, espe¬ 
cially those coming from the trunk, respiratory muscles and eyes. 
He tries as far as possible, to keep these sensations constant. On 
the other hand, Bt notes early in the course of the work the tendency 
to judge through classification of N and V. Later on he notes »I 
seem to place the norm in a series; i. e. when I see a norm I seem 
to recognize it as a member of a certain class, or as having seen it 
frequently before.« 
In the case of A1 there was a large amount of visual reproduc¬ 
tion during the 30 sec. and 60 sec. intervals, but for the smaller 
intervals reproduction was rarely noted. This reproduction was usually 
at once verbal and visual, and it was often impossible to say which